Influenza virus infection of neonates can lead to life-threatening disease. The rate of LRTI-associated hospitalizations is >4 times higher in children less than 1 year of age compared to those between 1 and 4 years and infants younger than 6 months of age are particularly vulnerable to the development of severe disease. Current influenza vaccines on the market are not approved for infants <6 months of age as a result of their limited effectiveness in this age group. Overcoming this poor responsiveness will require development of vaccines with greater immunogenicity in this population. Another important area of investigation is the ability of infants to respond to universal vaccines designed to provide protection across multiple strains of influenza. While targeting production of these antibodies by vaccination is highly desirable, our understanding of how effectively newborns can produce them or the accessory signals that can optimally elicit these antibodies is unknown. The ultimate goal of the studies proposed in this application is to identify a vaccine approach for influenza that is safe and broadly protective when delivered to neonates. To evaluate potential strategies, we will use our established African green monkey (AGM) nonhuman primate neonate model. Using this model we previously found that conjugation of the TLR7/8 agonist R848 to inactivated influenza promotes significant increases in virus-specific IgG and IFN?-producing T cell responses, providing rationale for the continued exploration of this adjuvant in neonates. We will utilize R848 together with heterologous boost or an HA stem construct as approaches to elicit broadly reactive antibody. As part of our analyses we will evaluate the role of Tfh responses in modulating broadly reactive antibody quantity and quality. The results of these studies will provide mechanistic as well as practical information that may lead to the improved design of vaccines that will be efficacious in the vulnerable neonate population.